Protonating Tricarboxybenzenes

May 1, 2022| Chemist
Protonating Tricarboxybenzenes

Tricarboxybenzenes were (tri-)protonated, resulting in the formation of astonishingly stable species. The different isomers are stabilized by mesomerism and hyperconjugation depending on the substitution pattern. These effects are observable by X-ray diffraction and NMR spectroscopy and also computable by NPA and NICS calculations, enabling qualitative and quantitative statements.

Triprotonation of 1,3,5-tricarboxybenzene was achieved in the superacidic systems HF/SbF5 and HF/AsF5. The starting material began dissolving at −20 °C, achieving a complete solution at 0 °C. Removal of the solvent at −78 °C led to the formation of colorless solids, respectively.

Triprotonation of the three constitution isomers of tricarboxybenzene was accomplished. Furthermore, the preparation of selected mono- and dications showed the sequence of protonation steps. The cations were mostly isolated as [SbF6] and [AsF6] species, which were characterized by Raman and NMR spectroscopy as well as X-ray structure determination. To further elucidate the experimental results, quantum chemical calculations are employed, especially in regard to charge distribution with NPA charges and aromaticity by NICS(0) values. Thermal decomposition of the compounds was investigated in order to explore the possibility of acyl cation formation. The influence of the aromatic system, substitution pattern and anomeric effect concerning the properties of the respective compounds was thus explained.

DOI: 10.1002/ejoc.202101488

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